1. Field of the Invention
This invention relates to a mold clamp mechanism for tire press, which is simplified in construction and operation and which can clamp molds promptly in a facilitated manner to ensure high efficiency.
2. Description of the Prior Art
A tire press is usually provided with upper and lower molds which are movable toward and away from each other, a dome which circumvents the upper and lower molds and a shaping center mechanism, and is supplied with steam or other pressurized heat medium for shaping and curing tires. In the shaping and curing operation, the upper and lower molds have to be securely clamped in a closed state against the pressurized medium which is supplied through a bladder of the center mechanism. In this regard, it has been the conventional practice to fix the lower mold on the base of a curing machine through a heat insulator and a lower platen (internally heated) by bolt clamp means which engages peripheral edge portions of the mold, while fixing the upper mold by similar bolt clamp means on an upper platen which is retained on part of the top platen. However, such bolt clamp means requires time for mold replacements and creates extremely bad working conditions for workers since the molds have to be replaced while they are still very hot. In addition, the job of fastening large bolts involves relatively heavy labor, resulting in a longer press cycle and lower productivity. Especially in the case of a press of the type in which the outer peripheries of the molds are covered by a dome, the space around the outer peripheries of the molds is extremely limited and therefore installation and operation of such bolt clamp means usually give rise to various difficulties. In place of the manual clamp means, the applicant proposed an automatic clamp means in Laid-Open Japanese Patent Application No. 57-167237, for clamping the lower mold of the mold set on a tire press. More particularly, the lower mold in the prior application is provided with a plurality of engaging portions in its outer peripheral portions, and clamp rods with engaging portions for releasably clamping the lower mold in position are movable up and down in the axial direction by means of a lift drive (i.e., a fluid cylinder) and at the same time rotatable about their axes by means of a rotational drive (i.e., a fluid cylinder). The clamp rods are driven into clamping and releasing positions by forward and reverse rotations of the rotational drive to couple and uncouple the engaging portions, and at the same time are driven up and down by the lift drive to clamp the lower mold to the base of the tire press. This automatic clamp mechanism requires the formation of recessed engaging portions in the outer peripheral portions of the lower mold and the employment of a couple of fluid cylinders for the lifting and rotating movements. The mold structure with a plurality of recessed or notched engaging portions around its marginal edge involves problems with regard to the mold strength. On the other hand, the provision of a couple of fluid cylinders for each clamp rod results in complication in construction and maintenance in addition to an increase in size. Such further involves problems in that the clamp is loosened immediately and the lower mold floats up if the fluid pressure in the drive cylinder drops, and in that it is difficult to mount the cylinders in narrow limited spaces around the molds or in a lower portion of the press. A difficulty is also encountered in operating the two cylinders in an appropriately timed manner.